1. Field of the Invention
This invention pertains to liquid filtering and heating apparatus. More particularly, it relates to liquid filter-heater combinations which have particular utility in connection with the operation of swimming pools.
2. Prior Art
Swimming pools, of the type wherein the same water is recirculated, have long had associated with them filtration apparatus for removing solid impurities from the water. It has also been customary to heat swimming pool water in those installations where it is desired to extend the length of the swimming season. Such heating would seek, for example, to raise the temperature of the swimming pool water from an ambient of 76.degree.F to a desired temperature of 82.degree.F. Most usually, the heating is achieved with a water heater generally resembling a domestic hot water heater.
More recently, it has been recognized that economies in initial equipment cost and subsequent operating expenses may be realized by combining a filter with a heater to produce what may be termed a filter-heater combination. Such apparatus is shown in my own prior U.S. Pat. Nos. 3,139,067 and 3,386,419 granted, respectively, on June 30, 1964 and June 4, 1968.
However, combined units of this type have their own particular problems. Since they are frequently located proximate swimming pools, as distinguished from in locked boiler rooms, it is important that they not present a hazard by virtue of hot external surfaces or high temperature gas emissions. While the unit can be protectively housed, this adds nothing but expense. Another problem has to do with condensation and consequent corrosion within the combustion chamber which is the natural result of having cold surfaces therein. Finally, if heat transfer is to be effected via heat exchangers (e.g. coils, fin-tubes and the like) these represent elements which are subject to clogging because of salt deposition and require periodic maintenance and replacement.